The present invention relates to black magnetic iron oxide particles and a magnetic toner, and more particularly, to black magnetic iron oxide particles having not only excellent blackness and electrification property, but also excellent environmental stability capable of maintaining a stable charge amount thereon even under low-temperature and low-humidity conditions or high-temperature and high-humidity conditions, and a magnetic toner using the black magnetic iron oxide particles.
The black magnetic iron oxide particles of the present invention have a black color and, therefore, are useful as black color pigments for paints, printing inks, rubber or resin compositions, or the like, and further as black magnetic particles for magnetic toner.
Magnetite particles are known as typical black pigments, and have been generally used for a long time as colorants for paints, printing inks, cosmetics, rubber or resin compositions, or the like.
In particular, the magnetite particles have been more frequently used as black magnetic iron oxide particles for magnetic toners of one component system in which composite particles obtained by mixing and dispersing black magnetic iron oxide particles in resin are used as a developer.
With recent tendency toward high-speed copying and high-image quality for laser beam printers or digital copying machines, it has been strongly required to improve properties of a magnetic toner used as a developer. For this purpose, the magnetic toner has been required to exhibit not only a sufficient blackness and an improved electrification property, but also an excellent environmental stability capable of maintaining a stable charge amount thereon without any adverse influence due to change in temperature or humidity.
Also, in order to satisfy the above requirements of the magnetic toner, it has been strongly required to improve properties of black magnetic iron oxide particles used in the magnetic toner.
Namely, in order to obtain magnetic toners exhibiting excellent blackness, electrification property and environmental stability, the black magnetic iron oxide particles used therein have been required not only to have a sufficient blackness and an adequate FeO content as well as more excellent dispersibility and electrical properties, but also to exhibit an excellent environmental stability.
It is known that the blackness of the black magnetic iron oxide particles varies depending upon the amount of Fe2+ (FeO) contained therein. Therefore, in order to obtain the particles having an excellent blackness, the FeO content thereof has been required to be large.
In the consideration of good electrical properties, it is preferred that the black magnetic iron oxide particles have a small FeO content. Namely, the electrical resistance value of the black magnetic iron oxide particles varies depending upon the FeO content. The larger the FeO content, the lower the electrical resistance value, so that it is difficult to use the black magnetic iron oxide particles as a starting material of the magnetic toner. Therefore, the black magnetic iron oxide particles are required not only to exhibit well-balanced blackness and electrical resistance, but also to have an adequate blackness and a high electrical resistance.
Also, the electrification property of the magnetic toner largely depends upon the surface conditions of the black magnetic iron oxide particles exposed to the surface of the magnetic toner. In particular, as described above, FeO contained in the black magnetic iron oxide particles acts for reducing an electrical resistance of the magnetic toner. Therefore, the electrification property of the magnetic toner is considerably influenced by the content of FeO and the distribution of FeO in each black magnetic iron oxide particle. In this regard, Japanese Patent Application Laid-Open (KOKAI) No. 4-338971 describes that xe2x80x9cthe distribution condition of Fe(II) in the surface layer of magnetic iron oxide more highly contributes to stable frictional electrification property of the obtained magnetic toner under various environmental conditions rather than the FeO contentxe2x80x9d.
The dispersibility of the black magnetic iron oxide particles largely depends upon the surface conditions thereof. Therefore, in order to improve the surface conditions of the black magnetic iron oxide particles and enhance the dispersibility thereof, it has been attempted to coat surfaces of the black magnetic iron oxide particles with a silicon compound, an aluminum compound or the like. In addition, the black magnetic iron oxide particles are fine particles and, therefore, tend to be magnetically agglomerated, resulting in the deterioration of the blending property with resins. Consequently, it has been required to prevent the black magnetic iron oxide particles from being magnetically agglomerated.
Further, the magnetic toner is required to exhibit stable properties even upon any change in environmental conditions, for example, under low-temperature and low-humidity conditions or under high-temperature and high-humidity conditions. For this reason, the black magnetic iron oxide particles used in the magnetic toner have been strongly required to have an excellent environmental stability and constantly exhibit a stable charge amount.
Hitherto, it has been attempted to improve various properties of the black magnetic iron oxide particles by incorporating different kinds of elements other than iron thereinto, and coating the surface thereof with a plurality of layers (Japanese Patent Application Laid-Open (KOKAI) Nos. 7-240306(1995), 7-267646(1995), 8-48524(1996), 8-50369(1996), 8-101529(1996), 11-157843(1999), 11-189420(1999), 11-314919(1999), 2000-239021, 2000-272923, 2000-335920, 2000-335921, 2000-344527, 2000-344528 and 2000-10821, or the like).
At present, it has been strongly demanded to provide black magnetic iron oxide particles satisfying various properties described above. However, black magnetic iron oxide particles capable of fulfilling these requirements cannot be obtained conventionally.
That is, Japanese Patent Application Laid-Open (KOKAI) No. 7-240306(1995) describes magnetic particles containing silicon inside thereof, having a co-precipitate of silica and alumina present on the surface thereof, and further having fine non-magnetic oxide particles or fine non-magnetic oxide hydroxide particles adhered onto the co-precipitate, which comprise an element selected from the group consisting of Fe, Ti, Zr, Si and Al. Thus, the magnetic particles have an outermost layer composed of the fine non-magnetic particles and, therefore, fail to form a ferrite structure, thereby failing to show an excellent environmental stability.
In Japanese Patent Application Laid-Open (KOKAI) No. 7-267646(1995), it is described that magnetite particles have an outer-shell portion containing at least one metal element selected from the group consisting of Zn, Mn, Cu, Ni, Co, Mg, Cd, Al, Cr, V, No, Ti and Sn. However, since the magnetite particles have a two phase structure, the electrical resistance value thereof is low, and the build-up of electrification and the electrification stability thereof are unsatisfactory.
Japanese Patent Application Laid-Open (KOKAI) No. 8-48524(1996) describes magnetite particles successively coated with an iron-zinc oxide thin film and an iron-silicon oxide thin film on the surface thereof. The magnetite particles show a low electrical resistance value since the outermost layer thereof is not composed of spinel iron oxide containing different kinds of metal elements. Further, the build-up of electrification as well as the electrification stability thereof are unsatisfactory.
Japanese Patent Application Laid-Open (KOKAI) No. 8-50369(1996) describes magnetic particles containing silicon locally present on the surface portion thereof and further containing Zn, Mg or Mn. However, the magnetic Particles not only show a low electrical resistance value, but also are unsatisfactory in build-up of electrification as well as electrification stability. Further, the magnetic particles fail to show an excellent environmental stability because of moisture-absorbing property thereof.
Japanese Patent Application Laid-Open (KOKAI) No. 8-101529(1996) describes magnetic particles coated with an iron-zinc oxide thin film. However, the magnetic particles not only show a low electrical resistance value, but also are unsatisfactory in build-up of electrification as well as electrification stability. In addition, the magnetic particles also fail to show an excellent environmental stability because of moisture-absorbing property thereof.
Japanese Patent Application Laid-Open (KOKAI) No. 11-157843(1999) describes magnetite particles containing silicon component continuously distributed from center to surface of each particle and exposed to the surface thereof, and having an outer-shell coat composed of a metal compound containing a metal component selected from the group consisting of Zn, Mn, Cu, Ni, Co, Cr, Cd, Al, Sn, Mg and Ti which is bonded to the silicon component. However, the magnetite particles fail to show a good build-up of electrification because of containing no metal component inside thereof.
Japanese Patent Application Laid-Open (KOKAI) No. 11-189420(1999) describes magnetite particles containing silicon and aluminum components continuously distributed from center to surface of each particle and exposed to the surface thereof, and having an outer-shell coat composed of a metal compound containing a metal component selected from the group consisting of Zn, Mn, Cu, Ni, Co, Cr, Cd, Sn, Mg and Ti which is bonded to the silicon and aluminum components. However, the magnetite particles also fail to show a good build-up of electrification because of containing no metal component inside thereof.
Japanese Patent Application Laid-Open (KOKAI) No. 11-314919(1999) describes magnetite particles having a first coat containing hydrated alumina or alumina sol, and a second coat formed on the first coat, which comprises silica particles produced from colloidal silica. However, since these coats are not ferrite, the magnetite particles exhibit a low electrical resistance value, and are unsatisfactory in build-up of electrification as well as electrification stability. Further, the magnetite particles fail to exhibit an excellent environmental stability because of moisture-absorbing property thereof.
Japanese Patent Application Laid-Open (KOKAI) No. 2000-239021 describes iron oxide particles coated with an Alxe2x80x94Fe composite oxide layer. However, the iron oxide particles exhibit a low electrical resistance value, and are unsatisfactory in build-up of electrification as well as electrification stability.
Japanese Patent Application Laid-Open (KOKAI) No. 2000-272923 describes iron oxide particles containing a silicon component continuously distributed from center to surface of each particle, and having a coating layer composed of a metal compound containing a metal component selected from the group consisting of Zn, Mn, Cu, Ni, Co, Cr, Cd, Al, Sn, Mg and Ti which is bonded to the silicon component, wherein a core portion thereof to which the silicon component is exposed, is coated with an Al component. Since the metal component is present in the form of an outer shell, the iron oxide particles show low residual magnetization, low coercive force and high electrical resistance, so that the charge amount thereof can be adequately controlled. However, the iron oxide particles are still insufficient in build-up of electrification.
Japanese Patent Application Laid-Open (KOKAI) No. 2000-335920 describes iron oxide particles containing at least one element selected from the group consisting of Mg, Na, K, Ca, Li, Ti, S, Al, Si, B and C wherein the total amount of the above elements contained in a portion extending inwardly from a surface of each particle which corresponds to not more than 80% by weight of the particle, is not less than 95% by weight based on the total weight of the elements contained in the particle. However, since the iron oxide particles are the raw particles for providing magnetic particles having a low specific gravity, the iron oxide particles are unsatisfactory in electrification property.
Japanese Patent Application Laid-Open (KOKAI) No. 2000-335921 describes iron oxide particles coated with a composite oxide thin film containing iron, silicon and at least one element selected from the group consisting of Al, Ce, Mo, W and P. However, the iron oxide particles are unsatisfactory in build-up of electrification.
Japanese Patent Application Laid-Open (KOKAI) No. 2000-344527 describes iron oxide particles having a composite oxide of Si and Fe present on the surface thereof, and Japanese Patent Application Laid-Open (KOKAI) No. 2000-344528 describes iron oxide particles having a lower coat composed of a composite oxide of Si and Fe and an upper coat composed of Al component. However, these iron oxide particles are still unsatisfactory in environmental stability since the particles are not coated with ferrite containing different kinds of metal elements.
Japanese Patent Application Laid-Open (KOKAI) No. 2001-10821 describes iron oxide particles having a coat composed of a composite oxide of zinc and iron, and further a coat formed on the composite oxide coat, which is composed of a composite oxide of zinc and iron or a zinc compound. However, the iron oxide particles fail to show an excellent electrification property.
As a result of the present inventors"" earnest studies, it has been found that black granular spinel iron oxide particles having a three-phase structure comprising a core portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles; a surface coat portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles; and an intermediate layer disposed between the core portion and the surface coat portion which substantially do not contain any of the above metal elements other than Fe, can exhibit not only excellent blackness and electrification property, but also excellent environmental stability capable of maintaining stable charge amount even under low-temperature and low-humidity conditions or high-temperature and high-humidity conditions. The present invention has been attained based on the finding.
An object of the present invention is to provide black magnetic iron oxide particles exhibiting not only excellent blackness and electrification property, especially excellent build-up of electrification, but also excellent environmental stability.
Another object of the present invention is to provide a magnetic toner exhibiting not only excellent blackness and electrification property, especially excellent build-up of electrification, but also excellent environmental stability.
A further object of the present invention is to provide a black color pigment for paints, printing inks, rubber or resin compositions, etc., having an excellent blackness.
To accomplish the aim, in a first aspect of the present invention, there are provided black magnetic iron oxide particles having a three-phase structure comprising:
a core portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles;
a surface coat portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles; and
an intermediate layer disposed between the core portion and the surface coat portion, containing substantially none of the metal elements other than Fe,
and having an average particle diameter of 0.05 to 1.0 xcexcm.
In a second aspect of the present invention, there are provided black magnetic iron oxide particles having an average particle diameter of 0.05 to 1.0 xcexcm and a three-phase structure comprising:
a core portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles;
a surface coat portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles; and
an intermediate layer disposed between the core portion and the surface coat portion, containing substantially none of the metal elements other than Fe,
and having a coating comprising an organic compound having a hydrophobic group formed on the surface coat portion.
In a third aspect of the present invention, there are provided black magnetic iron oxide particles having an average particle diameter of 0.05 to 1.0 xcexcm and a three-phase structure comprising:
a core portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles;
a surface coat portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles; and
an intermediate layer disposed between the core portion and the surface coat portion, containing substantially none of the metal elements other than Fe,
and having a coating comprising at least one compound selected from the group consisting of hydroxides of aluminum, oxides of aluminum, hydroxides of silicon and oxides of silicon on the surface coat portion.
In a fourth aspect of the present invention, there are provided black magnetic iron oxide particles having an average particle diameter of 0.05 to 1.0 xcexcm and a three-phase structure comprising:
a core portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles;
a surface coat portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles; and
an intermediate layer disposed between the core portion and the surface coat portion, containing substantially none of the metal elements other than Fe,
and having a coating comprising fine oxide particles composed of an element selected from the group consisting of Al, Si, Zr and Ti on the surface coat portion.
In a fifth aspect of the present invention, there are provided black magnetic iron oxide particles having an average particle diameter of 0.05 to 1.0 xcexcm and a three-phase structure comprising:
a core portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles;
a surface coat portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles; and
an intermediate layer disposed between the core portion and the surface coat portion, containing substantially none of the metal elements other than Fe,
and having a coating comprising fine oxide particles coated with at least one compound selected from the group consisting of methylsilane, trimethylsilane and octylsilane on the surface coat portion.
In a six aspect of the present invention, there is provided a magnetic toner comprising a binder resin and black magnetic iron oxide particles having a three-phase structure comprising:
a core portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles;
a surface coat portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles and
an intermediate layer disposed between the core portion and the surface coat portion, containing substantially none of the metal elements other than Fe,
and having an average particle diameter of 0.05 to 1.0 xcexcm.
In a seventh aspect of the present invention, there is provided a black color pigment comprising black magnetic iron oxide particles having a three-phase structure comprising:
a core portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles;
a surface coat portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles; and
an intermediate layer disposed between the core portion and the surface coat portion, containing substantially none of the metal elements other than Fe,
and having an average particle diameter of 0.05 to 1.0 xcexcm.
In an eighth aspect of the present invention, there are provided black magnetic iron oxide particles having an average particle diameter of 0.05 to 1.0 xcexcm and a three-phase structure comprising:
a core portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles;
a surface coat portion containing at least one metal element other than Fe selected from the group consisting of Mn, Zn, Cu, Ni, Cr, Cd, Sn, Mg, Ti, Ca and Al in an amount of 0.1 to 10% by weight based on whole Fe contained in the particles; and
an intermediate layer disposed between the core portion and the surface coat portion, containing substantially none of the metal elements other than Fe,
wherein a silicon compound is present in the intermediate layer, the surface coat portion, or the intermediate layer and the surface coat portion of the black magnetic iron oxide particles.